1. The Field of the Invention
The field of art to which this invention pertains is valve lifters for and used in combination with internal combustion engines.
2. Description of the Prior Art
Perhaps the greatest cause of operating problems associated with the conventional hydraulic valve lifter on prime mover engines is piston movement. Too much can cause lifter wear and impact damage to the other elements and too little can cause valve burn out. Besides field maintenance problems such as improper purging of air out of the pressure chamber, no make-up oil, improper adjustments for operating range, etc., the means of metering the oil out of the pressure chamber causes improper piston movement. Generally, the metering is accomplished in the space between the piston and cylinder. These surfaces are subject to wear which will in time change the metering rate. Also these surfaces must be precision machined to accommodate the required sliding fit and hold a clearance for the oil to be metered through it. With such arrangment, the lifter collapse rate range, which is directly related to the metering action, is very narrow.